Bitmap format Analysis

Let's take a look at the bitmap file (*. BMP) format. The bitmap file is divided into the following 3 parts:

Block name	Corresponds to the Windows fabric Body Definition	Size (Byte)
File Information Header	Bitmapfileheader	14
Bitmap Information Header	Bitmapinfoheader	40
RGB Color Array	byte*	Determined by the image's long and wide dimensions

1.file Information header Bitmapfileheader The structure is defined as follows:typedef struct TAGBITMAPFILEHEADER {/* BMFH * /UINT Bftype;
DWORD bfsize;
UINT bfReserved1;
UINT BfReserved2;
DWORD bfoffbits;} Bitmapfileheader;among them:

bftype	< Span style= "font-size:medium;" > Description of the file type, which must be 0x4d42, which is the character ' BM '.
bfsize
bfreserved1	reserved, must be set to 0
bfreserved2	< Span style= "font-size:medium;" > reserved, must be set to 0
bfoffbits

2. Bitmap Information Header Bitmapinfoheader The structure is defined as follows:typedef struct TAGBITMAPINFOHEADER {/* BMIH * /DWORD bisize;
LONG biwidth;
LONG biheight;
WORD biplanes;
WORD biBitCount;
DWORD bicompression;
DWORD biSizeImage;
LONG Bixpelspermeter;
LONG Biypelspermeter;
DWORD biclrused;
DWORD biclrimportant;} bitmapinfoheader;among them:

Bisize	Describes the number of words required for the bitmapinfoheader structure.
Biwidth	Indicates the width of the image, in pixels.
Biheight	Indicates the height of the image, in pixels. Note: This value, in addition to describing the height of the image, has another use to indicate whether the image is a backward bitmap or a forward bitmap. If the value is a positive number, the image is inverted, and if the value is a negative number, the image is positive. Most BMP files are inverted bitmaps, that is, when the height value is a positive number.
biplanes	Describes the number of bits for the target device, and its value will always be set to 1.
biBitCount	Indicates the number of bits/pixels, with values of 1, 4, 8, 16, 24, or 32. However, since most of the images we use are 24-bit and 32-bit, we discuss these two types of images.
Bicompression	Describe the type of image data compression, and we only discuss types that are not compressed:Bi_rgb.
biSizeImage	Indicates the size of the image, in bytes. When in bi_rgb format, it can be set to 0.
Bixpelspermeter	Describes the horizontal resolution, expressed in pixels / meters.
Biypelspermeter	Describes the vertical resolution, expressed in pixels / meters.
biClrUsed	Describes the number of color indexes in the color table that the bitmap is actually using (set to 0 , which means that all palette items are used).
Biclrimportant	Indicates that the number of color indexes that have a significant effect on the image display, if 0, is important.

3. RGB Color Arrayabout RGB tri-color space I think everyone is very familiar with, here I want to say is under Windows ,RGB color array storage format actually BGR. In other words , the RGB bit image format for the four bits is:

Blue B value

Green G value

Red R value

for the three-bit RGB bit image, the format of the voxel data is:

Blue B value

Green G value

Red R value

Transparent channel A value

The transparent channel is also called the Alpha channel, which is a transparent property of the pixel, with a value between 0(fully transparent) and 255(opaque). For The image of the position, the entire image is opaque because there is no Alpha channel. Line Alignmentbecause Windows has a minimum of 4 bytes in a row scan, whenpicture width × number of bytes per pixel! = integer multiples of 4 fill in the missing bytes at the back of each line with a 0 padding (generally not justified if the image width is a power of 2 ). Note:The first line of the RGB data for a BMP file represents the last line of data in the LCD

Bitmap format Analysis